The proposed research is designed to study certain of the biochemical and physiological processes that are fundamental to the maintenance of a normally functional cornea. In order that the tissue be transparent a constant level of hydration must be maintained in the stroma, and this necessitates the continuous active extrusion of water across the endothelium. Accordingly, the metabolism of this cell layer will be investigated, especially with regard to a glycopeptide, which we call labellein, that is suspected to be of importance in the movement of ions out of the cells. In order that the integrity of the epithelium be maintained constant replacement of cells lost by desquamation is necessary. This replication requires considerable metabolic activity which is dependent on substrates derived almost entirely from the aqueous humor. Therefore the mode of entry of substrates into the cornea will be studied. This knowledge will allow assessment of the adequacy of nutrient sources under conditions of deprivation or excessive demand.